quic/api: SharedThreadedPacketWriter — cross-thread batched UDP writer#450
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quic/api: SharedThreadedPacketWriter — cross-thread batched UDP writer#450afrind wants to merge 3 commits into
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Uses eventfd on Linux (EFD_NONBLOCK; counter semantics coalesce multiple flush() calls) and a non-blocking self-pipe on macOS. Wraps a lock-free folly::ProducerConsumerQueue for the data path. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Defines the write/flush/getResult contract for pluggable packet writers. BufQuicBatchResult is moved from IoBufQuicBatch.h to break an include cycle (IoBufQuicBatch → QuicBatchWriter → StateData). Adds conn.packetWriter (unique_ptr<QuicPacketWriter>) to QuicConnectionStateBase; null on all existing paths. Conditionalizes write/flush sites on packetWriter so the inline path is unchanged when no writer is installed. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Drains an EventFdQueue<PacketEntry> on a dedicated EventBase, batching
packets with writemGSO and UDP_SEGMENT (GSO) coalescing where supported.
Key design points:
- GSO chains are restricted to same-connection packets; connIds_ is a flat
per-slot vector (one entry per mmsg slot, the chain-opener's connId).
segsInChain tracks the segment count per chain so the maxSegmentsPerMsg
cap is applied to segments appended, not the mmsg slot index.
- Drain-thread arrays (bufs_, addrs_, opts_, connIds_, segCounts_) are
preallocated to maxMsgsPerCall_ at construction; no per-batch heap
allocation.
- bufs_ is preserved across EAGAIN so retryAndDrain resends the identical
batch via EPOLLOUT without rebuilding.
- maxMsgsBeforeYield (default 10) controls drain-thread fairness.
ConnectionPacketWriter is a per-connection adaptor that forwards write/flush
to the shared writer with the connection's connId attached.
QuicTransportBaseLite gains scheduleWrite() to let the drain thread signal
the connection EVB when the producer should resume after backpressure.
Six USDT tracepoints (shared_packet_writer_{queue_full,enqueue,batch_result,
partial_send,drain_done,yield}) instrument the enqueue and drain paths.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
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Drains an EventFdQueue on a dedicated EventBase, batching
packets with writemGSO and UDP_SEGMENT (GSO) coalescing where supported.
Key design points:
per-slot vector (one entry per mmsg slot, the chain-opener's connId).
segsInChain tracks the segment count per chain so the maxSegmentsPerMsg
cap is applied to segments appended, not the mmsg slot index.
preallocated to maxMsgsPerCall_ at construction; no per-batch heap
allocation.
batch via EPOLLOUT without rebuilding.
ConnectionPacketWriter is a per-connection adaptor that forwards write/flush
to the shared writer with the connection's connId attached.
QuicTransportBaseLite gains scheduleWrite() to let the drain thread signal
the connection EVB when the producer should resume after backpressure.
Six USDT tracepoints (shared_packet_writer_{queue_full,enqueue,batch_result,
partial_send,drain_done,yield}) instrument the enqueue and drain paths.